CIP2A facilitates the G1/S cell cycle transition via B-Myb in human papillomavirus 16 oncoprotein E6-expressing cells

A novel camptothecin derivative, ZBH-01, exhibits superior antitumor efficacy than irinotecan by regulating the cell cycle

BACKGROUND

Irinotecan (CPT-11) is a classic chemotherapeutic agent that plays an important role in the clinical treatment of metastatic colon cancer and other malignant tumors. We previously designed a series of novel irinotecan derivatives. In this study, we select one representative, ZBH-01, to investigate its sophisticated antitumor mechanism in colon tumor cells.

METHODS

The cytotoxic activity of ZBH-01 on colon cancer cells was evaluate by MTT or Cell Counting Kit-8 (CCK8) assay, 3D and xenograft model. The inhibitory effect of ZBH-01 on TOP1 was detected by DNA relaxation assay and Immuno Complex of Ezyme (ICE) bioassay. The molecular mechanism of ZBH-01 was explored by Next-Generation Sequencing (NGS), bioinformatics analyses, flow cytometry, qRT-PCR, and western blot etc. RESULTS: ZBH-01 can induce obvious DNA damage and has superior antitumor activity against colon cancer cells compared to CPT-11 and SN38 (7-Ethyl-10-hydroxy camptothecin, the in vivo active form of CPT-11) both in vivo and in vitro. Its inhibitory effect on topoisomerase I (TOP1) was also comparable with these two control drugs. There are a much larger number of 842 downregulated and 927 upregulated mRNAs in ZBH-01 treatment group than that in the controls. The most significantly enriched KEGG pathways for these dysregulated mRNAs were DNA replication, the p53 signaling pathway, and the cell cycle. After constructing a protein-protein interaction (PPI) network and screening out a prominent cluster, 14 involved in the cell cycle process was identified. Consistently, ZBH-01 induced G0/G1 phase arrest in colon cancer cells, while CPT-11/SN38 caused S phase arrest. The initiation of apoptosis by ZBH-01 was also superior to CPT-11/SN38, followed by the increased expression of Bax, active caspase 3, and cleaved-PARP, and decreased expression of Bcl-2. Additionally, CCNA2 (cyclin A2), CDK2 (cyclin-dependent kinase 2), and MYBL2 (MYB proto-oncogene like 2) might be involved in the G0/G1 cell cycle arrest induced by ZBH-01.

CONCLUSIONS

ZBH-01 can be an antitumor candidate drug for preclinical study in the future.

From Basic Science to Clinical Practice: The Role of Cancerous Inhibitor of Protein Phosphatase 2A (CIP2A)/p90 in Cancer

Cancerous inhibitor of protein phosphatase 2A (CIP2A), initially reported as a tumor-associated antigen (known as p90), is highly expressed in most solid and hematological tumors. The interaction of CIP2A/p90, protein phosphatase 2A (PP2A), and c-Myc can hinder the function of PP2A toward c-Myc S62 induction, thus stabilizing c-Myc protein, which represents a potential role of CIP2A/p90 in tumorigeneses such as cell proliferation, invasion, and migration, as well as cancer drug resistance. The signaling pathways and regulation networks of CIP2A/p90 are complex and not yet fully understood. Many previous studies have also demonstrated that CIP2A/p90 can be used as a potential therapeutic cancer target. In addition, the autoantibody against CIP2A/p90 in sera may be used as a promising biomarker in the diagnosis of certain types of cancer. In this Review, we focus on recent advances relating to CIP2A/p90 and their implications for future research.

Phosphorylation of RCC1 on Serine 11 Facilitates G1/S Transition in HPV E7-Expressing Cells

Persistent infection of high-risk human papillomavirus (HR-HPV) plays a causal role in cervical cancer. Regulator of chromosome condensation 1 (RCC1) is a critical cell cycle regulator, which undergoes a few post-translational modifications including phosphorylation. Here, we showed that serine 11 (S11) of RCC1 was phosphorylated in HPV E7-expressing cells. However, S11 phosphorylation was not up-regulated by CDK1 in E7-expressing cells; instead, the PI3K/AKT/mTOR pathway promoted S11 phosphorylation. Knockdown of AKT or inhibition of the PI3K/AKT/mTOR pathway down-regulated phosphorylation of RCC1 S11. Furthermore, S11 phosphorylation occurred throughout the cell cycle, and reached its peak during the mitosis phase. Our previous data proved that RCC1 was necessary for the G1/S cell cycle progression, and in the present study we showed that the RCC1 mutant, in which S11 was mutated to alanine (S11A) to mimic non-phosphorylation status, lost the ability to facilitate G1/S transition in E7-expressing cells. Moreover, RCC1 S11 was phosphorylated by the PI3K/AKT/mTOR pathway in HPV-positive cervical cancer SiHa and HeLa cells. We conclude that S11 of RCC1 is phosphorylated by the PI3K/AKT/mTOR pathway and phosphorylation of RCC1 S11 facilitates the abrogation of G1 checkpoint in HPV E7-expressing cells. In short, our study explores a new role of RCC1 S11 phosphorylation in cell cycle regulation.

The Nuclear Farnesoid X Receptor Reduces p53 Ubiquitination and Inhibits Cervical Cancer Cell Proliferation

The role of farnesoid X receptor (FXR) in cervical cancer and the underlying molecular mechanism remain largely unknown. Therefore, this study aimed to assess the mechanism of FXR in cervical cancer. Western blot, qRT-PCR, and immunohistochemistry demonstrated that FXR was significantly reduced in squamous cell carcinoma tissues, although there were no associations of metastasis and TNM stage with FXR. In Lenti-FXR cells obtained by lentiviral transfection, the overexpression of FXR reduced cell viability and colony formation. Compared with the Lenti-Vector groups, the overexpression of FXR induced early and late apoptosis and promoted G1 arrest. With time, early apoptosis decreased, and late apoptosis increased. In tumor xenograft experiments, overexpression of FXR upregulated small heterodimer partner (SHP), murine double minute-2 (MDM2), and p53 in the nucleus. Co-immunoprecipitation (Co-IP) showed that SHP directly interacted with MDM2, which is important to protect p53 from ubiquitination. Nutlin3a increased MDM2 and p53 amounts in the Lenti-Vector groups, without effects in the Lenti-FXR groups. Silencing SHP reduced MDM2 and p53 levels in the Lenti-FXR groups, and Nutlin3a counteracted these effects. Taken together, these findings suggest that FXR inhibits cervical cancer via upregulation of SHP, MDM2, and p53.

Markers of Angiogenesis, Lymphangiogenesis, and Epithelial-Mesenchymal Transition (Plasticity) in CIN and Early Invasive Carcinoma of the Cervix: Exploring Putative Molecular Mechanisms Involved in Early Tumor Invasion

The establishment of a proangiogenic phenotype and epithelial-to-mesenchymal transition (EMT) are considered as critical events that promote the induction of invasive growth in epithelial tumors, and stimulation of lymphangiogenesis is believed to confer the capacity for early dissemination to cancer cells. Recent research has revealed substantial interdependence between these processes at the molecular level as they rely on common signaling networks. Of great interest are the molecular mechanisms of (lymph-)angiogenesis and EMT associated with the earliest stages of transition from intraepithelial development to invasive growth, as they could provide the source of potentially valuable tools for targeting tumor metastasis. However, in the case of early-stage cervical cancer, the players of (lymph-)angiogenesis and EMT processes still remain substantially uncharacterized. In this study, we used RNA sequencing to compare transcriptomes of HPV(+) preinvasive neoplastic lesions and early-stage invasive carcinoma of the cervix and to identify (lymph-)angiogenesis- and EMT-related genes and pathways that may underlie early acquisition of invasive phenotype and metastatic properties by cervical cancer cells. Second, we applied flow cytometric analysis to evaluate the expression of three key lymphangiogenesis/EMT markers (VEGFR3, MET, and SLUG) in epithelial cells derived from enzymatically treated tissue specimens. Overall, among 201 differentially expressed genes, a considerable number of (lymph-)angiogenesis and EMT regulatory factors were identified, including genes encoding cytokines, growth factor receptors, transcription factors, and adhesion molecules. Pathway analysis confirmed enrichment for angiogenesis, epithelial differentiation, and cell guidance pathways at transition from intraepithelial neoplasia to invasive carcinoma and suggested immune-regulatory/inflammatory pathways to be implicated in initiation of invasive growth of cervical cancer. Flow cytometry showed cell phenotype-specific expression pattern for VEGFR3, MET, and SLUG and revealed correlation with the amount of tumor-infiltrating lymphocytes at the early stages of cervical cancer progression. Taken together, these results extend our understanding of driving forces of angiogenesis and metastasis in HPV-associated cervical cancer and may be useful for developing new treatments.

Computational analysis of TP53 mutational landscape unveils key prognostic signatures and distinct pathobiological pathways in head and neck squamous cell cancer

Background

Mutations of the tumour-suppressor gene TP53 are the most frequent somatic genomic alterations in head and neck squamous cell carcinoma (HNSCC). However, it is not yet clear whether specific TP53 mutations bear distinct clinical and pathophysiological significance in different HNSCC subgroups.

Methods

A systematic bioinformatics appraisal of TP53 mutations was performed on 415 HNSCC cases available on The Cancer Genome Atlas (TCGA). The following features were analysed and correlated with known clinicopathological variables: mutational profile of TP53, location (within secondary structure and predicted domains of p53 protein) and well-known hotspot mutations. Interactome–genome–transcriptome network analysis highlighted different gene networks. An algorithm was generated to develop a new prognostic classification system based on patients’ overall survival.

Results

TP53 mutations in HNSCCs exhibited distinct differences in different anatomical sites. The mutational profile of TP53 was an independent prognostic factor in HNSCC. High risk of death mutations, identified by our novel classification algorithm, was an independent prognostic factor in TCGA HNSCC database. Finally, network analysis suggested that distinct p53 molecular pathways exist in a site- and mutation-specific manner.

Conclusions

The mutational profile of TP53 may serve as an independent prognostic factor in HNSCC patients, and is associated with distinctive site-specific biological networks.

Cip2a/miR-301a feedback loop promotes cell proliferation and invasion of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a highly aggressive breast cancer subtype and lacks effective targeted therapies. Cancerous inhibitor of protein phosphatase 2A (Cip2a) is an oncogene that is known to inhibit PP2A tumor suppressor activity in human malignancies. We previously demonstrated that Cip2a is a novel target for the treatment of TNBC. However, the functional roles of Cip2a in TNBC progression are still not fully characterized. In this study, we identified that miR-301a is a novel target of Cip2a in TNBC cell lines by miRNA microarray analysis. We found that Cip2a increases E2F1 expression, which in turn transcriptional activates miR-301a by occupying the miR-301a host gene SKA2 promoter. Moreover, we found that miR-301a level is significantly increased in TNBC tissues, and up-regulation of miR-301a is responsible for Cip2a-induced cell proliferation and invasion of TNBC cells. Furthermore, miR-301a feedback promotes the expression of Cip2a via activation of ERK/CREB signaling. Together, our study suggests an auto-regulatory feedback loop between Cip2a and miR-301a and this auto-regulatory loop might play an important role in TNBC progression.

PP2A: A Promising Biomarker and Therapeutic Target in Endometrial Cancer

Over the last decade, the use of targeted therapies has immensely increased in the treatment of cancer. However, treatment for endometrial carcinomas (ECs) has lagged behind, although potential molecular markers have been identified. This is particularly problematic for the type II ECs, since these aggressive tumors are usually not responsive toward the current standard therapies. Therefore, type II ECs are responsible for most EC-related deaths, indicating the need for new treatment options. Interestingly, molecular analyses of type II ECs have uncovered frequent genetic alterations (up to 40%) in PPP2R1A, encoding the Aα subunit of the tumor suppressive heterotrimeric protein phosphatase type 2A (PP2A). PPP2R1A mutations were also reported in type I ECs and other common gynecologic cancers, albeit at much lower frequencies (0-7%). Nevertheless, PP2A inactivation in the latter cancer types is common via other mechanisms, in particular by increased expression of Cancerous Inhibitor of PP2A (CIP2A) and PP2A Methylesterase-1 (PME-1) proteins. In this review, we discuss the therapeutic potential of direct and indirect PP2A targeting compounds, possibly in combination with other anti-cancer drugs, in EC. Furthermore, we investigate the potential of the PP2A status as a predictive and/or prognostic marker for type I and II ECs.

Over Expressed TKTL1, CIP-2A, and B-MYB Proteins in Uterine Cervix Epithelium Scrapings as Potential Risk Predictive Biomarkers in HR-HPV-Infected LSIL/ASCUS Patients

High oncogenic risk human papillomaviruses (HR-HPVs) promote cervical carcinoma development, the fourth most common feminine cancer. A slow oncodevelopmental phase—defined histopathologically as Cervical Intraepithelial Neoplasia (CIN) grades 1–3, or cytologically as Low- or High-grade Squamous Intraepithelial Lesions (LSIL or HSIL)—precedes the malignancy. Cervical carcinoma screenings through HR-HPV genotyping and Pap smears are regularly performed in Western countries. Faulty cytology screening or genotyping or patients' non-compliance with follow-ups can let slip an oncoprogression diagnosis. Novel biomarker tests flanking HR-HPV genotyping and cytology could objectively predict the risk of disease progression thus helping triage LSIL/ASCUS patients. Here, anonymized leftovers of fresh cervical epithelium scrapings from twice (LSIL/ASCUS and HR-HPV DNA)-positive and twice (Pap smear- and HR-HPV DNA)-negative (control) patients in a proteome-preserving solution served to assess the biomarker worth of three cervical carcinoma-related proteins, i.e., B-MYB (or MYBL2), Cancerous Inhibitor of PP2A (CIP-2a), and transketolase-like1 (TKTL1). Leftovers anonymity was strictly kept and storage at −80°C, protein extraction, immunoblotting, and band densitometry were blindly performed. Only after tests completion, the anonymous yet code-corresponding HR-HPV-genotyping and cytology data allowed to assign each sample to the twice-positive or twice-negative group. Descriptive statistics showed that the three proteins levels significantly increased in the twice-positive vs. twice-negative scrapings. Diagnostic ROC curve analysis identified each protein's Optimal Decision Threshold (OTD) showing that TKTL1 and CIP-2a are stronger risk predictive biomarkers (Sensitivity, 0.91–0.93; Specificity, 0.77–0.83) than B-MYB. Logistic Regression coupled with Likelihood-Ratio Tests confirmed that a highly significant relation links increasing TKTL1/CIP-2a/B-MYB protein levels in twice-positive cervical scrapings to the risk of HR-HPV-driven oncoprogression. Finally, a 3 year clinical follow-up showed that 13 patients (50% of total) of the twice-positive group with biomarker values over OTDs compliantly underwent scheduled colposcopy and biopsy. Of these, 11 (i.e., 84.7%) received a positive histological diagnosis, i.e., CIN1 (n = 5; 38.5%) or CIN2/CIN2+ (n = 6; 46,2%). Therefore, TKTL1/CIP-2a/B-MYB protein levels could objectively predict oncoprogression risk in twice (HR-HPV- and Pap smear)-positive women. Further studies will assess the translatability of these findings into clinical settings.

CIP2A facilitates the G1/S cell cycle transition via B-Myb in human papillomavirus 16 oncoprotein E6-expressing cells

Infection with high‐risk human papillomaviruses (HR‐HPVs, including HPV‐16, HPV‐18, HPV‐31) plays a central aetiologic role in the development of cervical carcinoma. The transforming properties of HR‐HPVs mainly reside in viral oncoproteins E6 and E7. E6 protein degrades the tumour suppressor p53 and abrogates cell cycle checkpoints. Cancerous inhibitor of protein phosphatase 2A (CIP2A) is an oncoprotein that is involved in the carcinogenesis of many human malignancies. Our previous data showed that CIP2A was overexpressed in cervical cancer. However, the regulation of CIP2A by HPV‐16E6 remains to be elucidated. In this study, we demonstrated that HPV‐16E6 significantly up‐regulated CIP2A mRNA and protein expression in a p53‐degradation‐dependent manner. Knockdown of CIP2A by siRNA inhibited viability and DNA synthesis and caused G1 cell cycle arrest of 16E6‐expressing cells. Knockdown of CIP2A resulted in a significant reduction in the expression of cyclin‐dependent kinase 1 (Cdk1) and Cdk2. Although CIP2A has been reported to stabilize c‐Myc by inhibiting PP2A‐mediated dephosphorylation of c‐Myc, we have presented evidence that the regulation of Cdk1 and Cdk2 by CIP2A is dependent on transcription factor B‐Myb rather than c‐Myc. Taken together, our study reveals the role of CIP2A in abrogating the G1 checkpoint in HPV‐16E6‐expressing cells and helps in understanding the molecular basis of HPV‐induced oncogenesis.